1. Field of the Invention
Embodiments of the present invention relates to energy generation from wind power using wind power plants assembled spatially to form a “wind farm.” In particular, embodiments relates to a wind farm, a method for operating control of wind power plants, a wind power plant, and a method for operating control of a wind power plant.
2. Discussion of Background Information
Wind power plants of the type of interest here comprise a pivoted rotor structure, which is typically formed by a pivoted rotor shaft, a rotor hub at one end of the rotor shaft, and one or more rotor blades (rotor vanes) projecting from the rotor hub in the radial direction.
The rotor structure of the wind power plant is set in rotation by the wind force. Usually the rotor rotation (mechanical energy) is converted into electric energy by an electric generator and this electric energy is fed, e.g., into an electric grid.
Wind power plants of this type can cause disturbances in the operation of radar systems. Radar radiation reflected by the rotor structure or the rotor blades thereof undergoes a double displacement, depending on the direction of incidence of the radar radiation and rotational position or rotational speed of the rotor structure. In the case of radar systems with moving target recognition, which evaluate double displacements of this type, this can lead undesirably to corresponding parts of the rotor structure, that is, e.g., rotor blades, being misinterpreted as “flying objects.” Because the rotor structure parts moving towards the radar system or away from the radar system cause double displacements in the reflected radar radiation, a target imaging may be produced on the radar screen that cannot be easily distinguished from a real flying target.
This problem is further intensified in that wind power plants are often installed in a spatial distribution of a plurality of such wind power plants (so-called “wind farm”). Over a wind farm formed by several wind power plants, the rotor structures of which over the entire wind farm area produce displays on the radar screen, real flying targets can be identified by the operator only with difficulty and in the worst case not at all, whereby, e.g., flight safety can be drastically reduced.
In the case of radar systems with constant false alarm rate (CFAR), a response sensitivity or a threshold value for the detection of a flying target is generally dependent on the reflected radar signals received. In practice, this means that high interference reflections from wind power plants increase the detection threshold value and thus could completely prevent the detection of a real flying target (with lower reflections).
The particularly interfering radar reflections on rotating rotor structural parts, such as rotor blades, take place primarily when these structural parts extend orthogonally to the direction of incidence of the radar radiation.
For example, for a wind power plant with a rotor structure pivoted about a horizontal axis and having rotor blades projecting radially therefrom, particularly interfering radar reflections result when a rotor blade is pointing vertically upwards or downwards.
In the case of such a very widespread “three-bladed” wind power plant type, that is, with three rotor blades distributed in the circumferential direction projecting from a rotor hub, the situation “rotor blade points upwards or downwards” thus applies six times during a complete 360° rotor rotation.
Through the rotation of the radar antenna of an air monitoring radar system, the wind power plants of a wind farm are not constantly illuminated, but periodically, only in a period that results from the rotational speed of the radar antenna, the spatial extension of the wind farm, the width of the antenna lobe and the distance of the wind farm from the radar system.
A high interference of the radar operation by the wind farm results when a rotor blade of at least one of the wind power plants is perpendicular during the chronological radar illumination intervals. Since this condition is met 6 times during a rotor rotation in the example under consideration here and a wind farm often has a larger number of wind power plants, when a wind farm is operated in the detection range of a radar system a high frequency of interference must be anticipated.
Two solution approaches are known from the prior art for the problem explained above:
In DE 10 2008 024 644 A1, for example, it is proposed to provide rotor blades at least in some regions in a radar-absorbing construction. However, the disadvantage with this approach is the associated reduction of the design freedom regarding the structure and material of the rotor blade.
Another approach to solving the problem lies when planning a wind farm in providing a spatial arrangement of the individual wind power plants that is advantageous relative to the location of a radar installation and with respect to the radar system parameters. Apart from a restriction of the design freedom for the wind farm (or for the radar system) associated therewith, the reduction of interference in the radar operation that can be achieved thereby is often unsatisfactory.